This invention relates generally to medical devices for measuring blood pressure and pertains more particularly to cuff-type systems employing a pump and transducers.
Many types of blood pressure measurement devices are known in the prior art. One example is U.S. Pat. No. 4,105,021 to Williams et al which shows a system for applying an occluding inflatable cuff to a body member, with the pressure applied thereby being cycled between a pressure greater than systolic and a pressure less than diastolic. The pressurization cycle described in this patent occurs as a controlled bleed of pressure from the occluding cuff during the time that a plurality of blood pressure pulses occur. The patent shows the use of a blood flow monitor and a pressure monitor to measure pressure inside the cuff. A similar system is described by Fletcher et al in U.S. Pat. No. 3,814,083, which describes a bleed-down of the cuff pressure which was from 160-60 mm Hg in 30 seconds. Both patents contemplate measuring both systolic and diastolic blood pressure during a single cycle of the occluding cuff pressure.
Blood pressure measurement systems are also described by Lichowsky in U.S. Pat. No. 3,905,354 which shows the measurement of pressure fluctuations in a chamber attached to a patient's arm, wherein the fluctuations correspond to heartbeats of the patient. Similarly, U.S. Pat. No. 4,074,711 to Link et al discloses a transducer for measuring the fluctuating component of a cuff pressure, which is representative of the pulsatile blood pressure.
A major problem with prior art methods of measuring blood pressure non-invasively is that the process of obtaining a measurement requires an undesirably long period of time. A problem faced with such prior art devices is that the user is unable to tell what the blood pressure is instantaneously and to tell how the blood pressure has changed over the period of a few heartbeats. A further problem faced by such prior art devices is that the accuracy of blood pressure measurements during a cuff pressure cycle may be degraded if the blood pressure is not steady.